This invention relates to augmentors for jet type powered aircraft and particularly to means to prefill the manifold with fuel to the several combustion zones at a precalculated time prior to light-off.
As is well known in high powered advance aircraft that employ augmentors it is abundantly important to prefill the manifold of each zone in the augmentor with fuel prior to light-off for obtaining immediate thrust response and smooth transition. Several techniques are exemplified by U.S. Pat. Nos. 3,587,231 granted to G. A. Fisher and C. F. Stearns on June 28, 1971; 3,552,123 granted to D. E. Anschutz and K. L. Linebrink on Jan. 5, 1971; and 3,331,204 granted to P. L. Love on July 18, 1967 where prefill was accomplished by mechanical means and the manifolds were prefilled from a separate fuel source which had a flow rate higher than the metering valve. In these instances, for example, mechanism was employed to sequentially prefill and hold by some latching arrangement until the next previous zone was connected to the metering valve. While such arrangements may be satisfactory for some aircraft applications or may meet the flight envelope of certain missions they are not satisfactory for others.
Hence, in order to maximize response time from a pilot's command signal as manifested by the throttle lever position, we have found that using the regular fuel source and fill valve timed according to preselected conditions, it is possible to increase the time responsiveness and achieve smooth transitions from one zone to the other. By knowing the volume of the manifold and the zone requested rate of fuel flow under the circumstances of limiting the rate of throttle lever signal to a predetermined rate of change, it is possible to calculate the time necessary to prefill the next subsequent combustion zone and hence the control would preopen the next zone fill valve so that the manifold would be filled when that zone is in the light-off condition. The rate limited throttle lever signal provides constant command rate so that timing can be consistently achieved at all flight conditions. This invention contemplates varying fuel flow for a given engine operation over the flight envelope.
In a partial advancement of the throttle lever, the throttle lever position would automatically determine that less than the full number of combustion zones would be actuated. Hence, the prefill would only be signaled to the fill valves for those zones that will fulfill the thrust requirements dictated by throttle lever position.